A III-Nitride device, such as a transistor, based on a III-Nitride heterojunction can typically exploit inherent piezoelectric and spontaneous polarization fields and subsequent generation of a two-dimensional electron gas (2DEG). For example, the inherent piezoelectric and spontaneous polarization fields and subsequent generation of the 2DEG can be exploited to form a high electron mobility transistor (HEMT).
In the III-Nitride device, as one example, an AlGaN barrier layer can be used to form an interface with a GaN channel layer. The 2DEG and high transconductance is formed near the interface of the GaN channel layer and the AlGaN barrier layer. To enhance mobility of the 2DEG, an AlN spacer layer can be formed between the GaN channel layer and the AlGaN barrier layer. Although the addition of the AlN spacer layer can be used to increase the piezoelectric charge at the interface with the GaN channel layer, it can have the deleterious effect of increasing the ohmic contact resistance of the III-Nitride device. Moreover, the addition of an AlN spacer layer may lead to poor morphological epitaxial growth, crystalline defect generation of any subsequent III-Nitride growth, including the AlGaN barrier layer, due to the increased mismatch in lattice constants caused by the higher Al content in the AlN spacer layer, and may even lead to undesirable warp, bow or ultimately cracking of the III-Nitride material and wafer.